I was on 80mg of Prozac for 4 months and gained 40lbs! I'm still struggling to lose the weight I gained from that med. I was on Wellbutrin at one point also but only experienced the side effects of the medication so I stopped taking it. Lamictal I found to be weight neutral, I even lost weight on Lamictal. I know how it feels to gain weight on a med, it truly sucks and really just depresses you more. I loved Prozac, for me that was it, I felt brand new. But the 40lb weight gain and only fitting into yoga pants didn't help with my depression.
Since you're going to a new doctor, see what they say. Maybe they just need to adjust your meds. It's really hard to tell when you're taking multiple medications which one is the cause of the weight gain. I agree with going for walks and getting plenty of sunshine. Good luck!! I know its tough.